Pressure monitoring circuits and methods

ABSTRACT

A pressure monitoring device comprises an analog-to-digital converter (ADC) to receive an analog signal and to convert the analog signal to a digital signal. The pressure monitoring device is configured to apply in a first state a first set of calibration coefficients to the digital signal, the first set of calibration coefficients being associated with a first pressure range. The pressure monitoring device is further configured to apply in a second state a second set of calibration values to the digital signal, the second set of calibration coefficients being associated with a second pressure range different than the first pressure range.

REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/955,105 which was filed on Nov. 29, 2010 and claims the benefit ofthe priority date of the above US application, the contents of which areherein incorporated in its full entirety by reference.

BACKGROUND

Pressure monitoring systems are used in many applications. For example,a tire pressure monitoring system (TPMS) often measures tire pressurefor a vehicle and notifies a vehicle's operator if the measured tirepressure falls outside of an ideal tire pressure range. Thus, a TPMSimproves safety for the vehicle operator and for surrounding vehicleoperators.

A TPMS for a vehicle often includes one tire pressure monitoring sensorper wheel, plus an electronic control unit (ECU). FIG. 1 shows anexample of a conventional tire pressure monitoring sensor 100, Thesensor 100 includes a pressure sensor 102, ananalog-to-digital-converter (ADC) 104, and a microcontroller 106. Duringoperation, the pressure sensor 102 provides an analog signal 108, andthe ADC 104 converts the analog signal 108 to a digital signal 110. Themicrocontroller 106 puts the digital signal into a formal suitable fortransmission to the ECU. The ECU then evaluates the formatted digitalsignal to determine whether the measured pressure falls within anacceptable tire pressure range, and can alert the driver if the pressurefalls outside this acceptable range.

Although conventional pressure monitoring systems are adequate in manyrespects, they suffer from a shortcoming in that they are unable toflexibly monitor different pressure ranges. For example, although onesensor is useful in measuring pressures for tires of passenger vehicles,which can have normal tire pressures in the range of about 100 kPa-450kPa; the same sensor is unable to effectively measure pressures fortires of commercial vehicles, which can have normal tire pressures inthe range of bout 100 kPa-850 kPa. Consequently, the present disclosureprovided improved methods and systems for monitoring pressure.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a conventional pressure sensorsystem;

FIG. 2 is a block diagram illustrating a pressure sensor system inaccordance with some embodiments of the present disclosure;

FIG. 3 is a plot illustrating functionality consistent with one exampleof FIG. 2's block diagram;

FIG. 4 is a flowchart illustrating a methodology consistent with oneexample of FIG. 2's block diagram;

FIG. 5 is a block diagram illustrating a pressure sensor system inaccordance with some embodiments of the present disclosure;

FIG. 6 is a plot illustrating functionality consistent with one exampleof FIG. 5's block diagram.

FIG. 7 is a block diagram of a dual-sensor module consistent with oneembodiment;

FIG. 8 is a flow chart illustrating a methodology consistent with oneexample of FIG. 7's block diagram.

DETAILED DESCRIPTION

The claimed subject matter is now described with reference to thedrawings, wherein like reference numerals are used to refer to likeelements throughout. In the following description, for purposes ofexplanation, numerous specific details are set forth in order to providea thorough understanding of the claimed subject matter. It may beevident, however, that the claimed subject matter may be practicedwithout these specific details.

In order to provide better resolution over a potentially wider pressurerange than previously available, the techniques disclosed herein set anoutput precision of an ADC based on a control signal provided by acontrol element. The control signal sets the output precision of the ADCto a first level to measure an ambient pressure within a first pressurerange; and signal sets the output precision of the ADC to a second levelto measure an ambient pressure within a second pressure range.

FIG. 2 shows a pressure monitoring system 300 in accordance with someembodiments of this disclosure. The pressure monitoring system 300includes a pressure sensor 302, a variable gain stage 304, an ADC 306, amicrocontroller 308, and a memory 310; which are operably coupled asshown. A timer 314, such as a watch-dog timer, can also be included insome implementations. In one embodiment, the microcontroller 308utilizes a calibration routine 312 (e.g., in the form of firmware storedin read-only memory or flash memory), wherein the calibration routine312 selects one of a number of sets of calibration coefficients 313 thatis specific to the pressure sensor 302 and devices included for aparticular pressure monitoring system (a number of sets of calibrationcoefficients 313 can be included to accommodate part-to-part variation).In some embodiments, the calibration coefficients 313 are stored in somesort of programmable, but not necessarily re-programmable, memory (e.g.,read-only memory, flash).

During operation, the pressure sensor 302 outputs an analog signal 316,wherein a signal level of the analog signal 316 is indicative of anambient pressure sensed by the pressure sensor 302. The variable gainstage 304 selectively adjusts the signal level of the analog signal 316based on a control signal 318 provided by the microcontroller 308. TheADC 306 then converts the analog signal having a selectively adjustedsignal level 320 into an N-bit digital value 322. Typical values for Nare 8, 9, 10, 11, or 12 bits, although N can be any integer numberranging in theory from 1 to infinity.

More particularly, if the control signal 318 is in a first state, thegain stage 304 adjusts the signal level of the analog signal 316according to a first gain, thereby tuning the N-bit output of the ADC306 to correspond to a first pressure range (e.g., 100 kPa-850 kPa usedfor commercial vehicles.) If the control signal 318 is in a secondstate, the gain stage 304 adjusts the signal level of the analog signal316 according to a second gain, thereby tuning the N-bit output of theADC 306 to correspond to a second pressure range (e.g., 100 kPa-450 kPaused for passenger vehicles.) In this way, the control signal 318provides a single pressure monitoring system with sufficient flexibilityto be used in a number of different applications.

FIG. 3 shows a more detailed example of a 3-bit ADC (e.g., ADC 306 inFIG. 2) consistent with FIG. 2's implementation. In this example, acontrol signal (e.g., control signal 318 in FIG. 2) changes the gain ofthe ADC between a first state and a second state to measure a firstpressure range 402 and a second pressure range 404, respectively.

When the control signal is in the first state during 402, the gain ofthe variable gain stage is set to a first level, causing the analoginput value of the ADC to range from 0V to 7V₁/8. Consequently, theeight unique digital output values of the ADC are approximately equallyspread over the entire first pressure range 402 (e.g., a first pressurerange for commercial vehicles having an ideal tire pressure ranging from100 kPa-850 kPa). Thus, the first output code can correspond to apressure measurement of 100 KPa, the second output code can correspondto a pressure measurement of 193.75 kPa, and so on such that the eighthpressure measurement is near the top of the first pressure range (e.g.,850 kPa).

When the control signal is in the second state during 404, the gain ofthe variable gain stage is set to a second level, causing the analoginput value to be “compressed”. In the illustrated example, the ADC nowranges from 0V to 2V₁/8 V. Consequently, the eight unique digital outputvalues of the ADC are approximately equally spread over the entiresecond pressure range (e.g., a second pressure range for passengervehicles having an ideal tire pressure ranging from 100 kPa-450 kPa).Thus, the first output code can correspond to a pressure measurement of100 KPa, the second output code can correspond to a pressure measurementof 143.75 kPa, the third output code can correspond to a pressuremeasurement of 187.5 kPa, and so on such that the eighth pressuremeasurement is near the top of the second pressure range (e.g., 450kPa).

Although FIG. 3 shows the lower boundary of the ADC at 0V, it will beappreciated that often a monitored pressure range will have a lowerboundary of other than 0V. The lower boundary of 0V has been chosensimply for ease of illustration and is in no way limiting.

FIG. 4 shows a method 500 consistent with one example carried out by thepressure monitoring system 300 of FIG. 2, although this methodologycould also be carried out using other pressure monitoring systems.

At 502, a microcontroller (e.g., microcontroller 308 in FIG. 2) canprogram a timer (e.g., timer 314 in FIG. 2) to assert an interrupt orwakeup signal at a predetermined time. The predetermined time can followa regularly spaced periodic pattern, or can occur at non-regularlyspaced intervals.

At 504, the timer “fires” at the predetermined time and the gain of avariable gain stage (e.g., variable gain stage 304 in FIG. 2) is set toa first level. The first level often corresponds to a first pressurerange.

At 506 while the gain is set to the first level, a pressure sensor(e.g., pressure sensor 302 in FIG. 2) takes a “raw” analog ambientpressure measurement.

At 508, the ADC transforms the analog signal to a first N-bit digitalvalue while the gain is set to the first level.

At 510, when this first N-bit digital value is read, a first set ofcalibration coefficients is applied to the first N-bit digital value toaccount for non-linearities and offset errors in the pressure sensorand/or ADC over the first pressure range (e.g., 100 kPa-450 kPa). Inthis way, a first calibrated N-bit digital value is provided. Note thatthere's no requirement that the number of bits in the calibrated digitalvalue area the same as the number of bits of ADC. For example, in oneimplementation, the ADC is 10 bits, yet the calibrated value is a 16-bitnumber.

At 512, the method 500 determines whether the first calibrated N-bitdigital value is within the first pressure range. If so (‘YES’ at 512),then no further processing is performed, and the method returns to 502or 504 to wait for the next predetermined time.

If the first calibrated measurement falls outside of the first pressurerange (‘NO’ at 512), then a second pressure measurement is performed inblocks 514-520—this time with a different gain setting for the variablegain stage. Often, the gain setting used during block 514-520 is greaterthan the gain setting used during 504-510 (i.e. first pressure range isa subset of the second pressure range).

More particularly, at 514, the gain of the variable gain stage is set toa second level. At 516, a second “raw” analog ambient pressuremeasurement is taken with the gain set to the second level. At 518, thesecond “raw” analog ambient pressure measurement is transformed into asecond N-bit digital value via the ADC. When this second N-bit digitalvalue is read, a second set of calibration coefficients is applied tothe second N-bit digital value to account for non-linearities and offseterrors in the pressure sensor and/or ADC over a second pressure range(e.g., 100 kPa-850 kPa), as shown in 520.

After 520, the method analyzes the first and second N-bit digitalvalues, and makes a determination which measured pressure is accurate.The microprocessor then determines whether the measured pressure fallsoutside of a specified pressure range. If the measured pressure isoutside of this specified range, the microcontroller can notify thevehicle operator or take other suitable remedial action to help ensurethat the unexpected pressure is suitably dealt with.

In some embodiments, rather than always performing two pressuremeasurements in a fixed sequence, the microcontroller can attempt to usethe same pressure range as was determined for the previous ambientpressure measurement. For example, if the microcontroller determines theambient pressure for one measurement falls within a 100 kPa-450 kPapressure range, the microcontroller can then take the next ambientpressure measurement under conditions for the same pressure range. Withthe assumption that the pressure inside the tire is changing slowly overtime, the previous range is more often than not the appropriate rangefor subsequent measurements, also. By taking only a single pressuremeasurement instead of two pressure measurements, such an implementationreduces power. A second measurement is taken only when themicrocontroller determines that the single pressure measurement may beerroneous.

Although pressure measurements as described above with regards to FIG. 4are taken only at predetermined times, in other embodiments the pressuresensor can monitor continuously without being triggered based on aninterrupt or periodic wakeup. However, because pressure often changesrelatively slowly and because such continuous monitoring tends toconsume more power, an interrupt based or periodic wakeup approach isoften more desirable.

FIGS. 5-6 show another embodiment wherein a pressure monitoring systemincludes a comparator 602 in addition to the previously discussedcomponents. Rather than carrying out two separate ambient pressuremeasurements (e.g., one pressure measurement assuming a first pressurerange and a second pressure measurement assuming a second pressure rangeas in FIG. 3's example), the comparator 602 acts as a control element toprovide a control signal 604 that notifies the microcontroller whetherthe ambient pressure is in the first or second pressure range.

FIG. 6 shows an example of how a comparator could be used in the contextof a 3-bit ADC. The comparator compares the level of the analog signalwith a threshold signal. If the control signal is in a first state(e.g., indicating the comparator detected the pressure was less than thethreshold), the microcontroller sets the variable gain stage to a firstgain level, such that the ADC output codes are spread approximatelyequally over the first pressure range. If the control signal is in asecond state (e.g., indicating the comparator detected the pressure wasgreater than the threshold), the microcontroller sets the variable gainstage to a second gain level, such that the ADC output codes are spreadapproximately equally over the second pressure range. Thus, inembodiments consistent with FIGS. 6-7, the control signal 604 acts as aflexible control bit.

FIG. 8 shows an embodiment of a dual sensor module 700 consistent withsome embodiments. The dual sensor module includes a first sensor 702(e.g., an accelerometer) and a second sensor 704 (e.g., a pressuresensor), although other embodiments can include more than two sensors.To take sensor measurements, the dual sensor module 700 also includes amultiplexer 706, a variable gain stage 708, an ADC 710, amicrocontroller 712, a memory unit 714 and a decoder/state machine 716.Although the first and second sensors 702, 704 are described withrespect to an accelerometer and a pressure sensor, respectively, it willbe appreciated that any type of sensor can be utilized in accordancewith this present disclosure.

During operation, the microcontroller 712 provides an N-bit sensorcontrol word on control bus 718 to the decoder/state machine 716. Forexample, in one embodiment the N-bit sensor control word can include5-bits and take the format shown in Table 1:

TABLE 1 Sample Sensor control word format Bit 5 (sensor type) 0 =acceleration 1 = pressure Bit 4 (pressure range) 0 = low pressure 1 =high pressure Bit 3 (automatic range selection) 0 = manual rangeselection 1 = automatic range selection Bits 2:1 (ADC gain) 00 = gain 7601 = gain 60 10 = gain 50 11 = gain 38

Thus, upon the decoder/state machine receiving the control word from themicrocontroller, the decoder/state machine can enable the proper blocksto carry out the functionality indicated by the control word.

FIG. 8 shows a method illustrating one example of how an N-bit controlword can induce functionality in the dual-sensor module consistent withFIG. 7.

At 802, the method analyzes the control word to determine the type ofsensor to be read. If the method determines an acceleration measurementis to be taken (‘YES’ at 802), then the method proceeds to 804 where itsets the gain of the ADC to a first level. Subsequently at 806, anacceleration measurement is taken by converting the analog voltage fromthe accelerometer to a digital value while the first gain level is usedfor the ADC.

In contrast if a pressure measurement is to be taken (‘NO’ at 802), themethod continues to 808 wherein it determines if manual or automaticpressure sensing is to be performed. If manual pressure sensing isselected (‘YES’ at 808), the method continues to 810 where the methodevaluates whether a low pressure range or a high pressure range is to beread. If the low pressure range is to be read (‘YES’ at 810), the ADCgain is set to a second level in 812 after which an analog voltage fromthe pressure sensor is converted to a digital value using the second ADCgain level at 814. If the high pressure range is to be read (‘NO’ at810), the ADC gain is set to a third level in 816 after which an analogvoltage from the pressure sensor is converted to a digital value usingthe third ADC gain level at 814.

If automatic pressure sensing is selected (‘NO’ at 808), the methodprogresses to 818 to determine whether a high pressure range or lowpressure range is to be read first. If the low range is to be read first(‘YES’) at 818, the gain level of the ADC is set to a second level at820, where the second ADC gain level can be different from the first ADCgain level (at 804). In 822, an analog voltage of the pressure sensor isconverted to a digital value. At 824, the method determines whether theambient pressure is greater than a high pressure threshold (PTh_High).If not (‘NO’ at 824), then the digital value from 822 is believed to becorrect and no further measurements are taken, thereby tending to limitpower. If so, however (‘YES’ at 824), then the method sets the ADC gainto a third level to carry out a high pressure measurement in 826. In828, an analog value is then read and converted into a digital valueusing the third ADC gain level.

If the high pressure range is to be read first (‘NO’ at 818), thenblocks 830-838 are followed. Notably, blocks 838 can utilize a differentpressure threshold PTh_Low (wherein PTh_Low is not necessarily the sameas PTh_High) to determine whether the high pressure measurement isreliable.

Although the disclosure has been shown and described with respect to oneor more implementations, equivalent alterations and modifications willoccur to others skilled in the art based upon a reading andunderstanding of this specification and the annexed drawings. Forexample, although examples illustrated herein show only two pressureranges, in other embodiments more than two pressure ranges can beincluded. Whatever the precise number of pressure ranges included, thepressure ranges can be entirely non-overlapping, partially overlapping,and/or may be spaced apart from one another. The pressure ranges be thesame size (e.g., have respective endpoints that share a commondifference therebetween) or can be different sizes (e.g., haverespectively endpoints that have different differences therebetween). Inaddition, the range of the ADC range can not only changed by a gainstage, it could also be changed by changing the number of bits N is thedigital output value.

The disclosure includes all such modifications and alterations and islimited only by the scope of the following claims. In particular regardto the various functions performed by the above described components(e.g., elements and/or resources), the terms used to describe suchcomponents are intended to correspond, unless otherwise indicated, toany component which performs the specified function of the describedcomponent (e.g., that is functionally equivalent), even though notstructurally equivalent to the disclosed structure which performs thefunction in the herein illustrated exemplary implementations of thedisclosure. In addition, while a particular feature of the disclosuremay have been disclosed with respect to only one of severalimplementations, such feature may be combined with one or more otherfeatures of the other implementations as may be desired and advantageousfor any given or particular application. In addition, the articles “a”and “an” as used in this application and the appended claims are to beconstrued to mean “one or more”.

Furthermore, to the extent that the terms “includes”, “having”, “has”,“with”, or variants thereof are used in either the detailed descriptionor the claims, such terms are intended to be inclusive in a mannersimilar to the term “comprising.”

What is claimed is:
 1. A pressure monitoring device comprising: ananalog-to-digital converter (ADC) to receive an analog signal and toconvert the analog signal to a digital signal; wherein the device isconfigured to apply in a first state a first set of calibrationcoefficients to the digital signal, the first set of calibrationcoefficients associated with a first pressure range and to apply in asecond state a second set of calibration coefficients to the digitalsignal, the second set of calibration coefficients associated with asecond pressure range different than the first pressure range, andwherein endpoints bounding the first pressure range are separated by afirst difference that is greater than a second difference separatingendpoints bounding the second pressure range.
 2. The device of claim 1,further comprising: a pressure sensor a variable gain stage between thepressure sensor and the ADC, wherein a control signal causes thevariable gain stage to change from a first gain to a second gain,thereby causing the change from the first state to the second state,respectively.
 3. The device of claim 2, further comprising a controlelement, wherein the control element comprises a microcontroller toprovide the control signal.
 4. The device of claim 3, wherein thecontrol element comprises a comparator to compare the analog signal witha pressure threshold, and wherein the change from the first state to thesecond state is based on the comparison.
 5. The device of claim 1,wherein the first and second sets of calibration coefficients accountfor non-linearities and/or other error contributors in the ADC andpressure sensor over the first and second pressure ranges, respectively.6. The device of claim 1, wherein the first pressure range fallsentirely within the second pressure range.
 7. The device of claim 1,wherein the first pressure range only partially overlaps the secondpressure range without falling entirely within the second pressurerange.
 8. The device of claim 1, wherein the first pressure range andsecond pressure range are non-overlapping.
 9. The device of claim 1,wherein neighboring unique output codes in the first pressure range arespaced apart by a first distance, and wherein neighboring unique outputcodes in the second pressure range are spaced apart by a seconddistance.
 10. A method of pressure monitoring, comprising: receiving ananalog pressure signal from a pressure sensor; converting the analogpressure signal to a digital signal by an analog-to-digital converter,applying, by a controller, in a first state corresponding to a firstpressure range measurement a first set of calibration coefficients tothe digital signal, and applying, by the controller, in a second statecorresponding to a second pressure range measurement a second set ofcalibration coefficients to the digital signal, wherein endpointsbounding the first pressure range are separated by a first differencethat is greater than a second difference separating endpoints boundingthe second pressure range.
 11. The method of claim 10, furthercomprising: upon receiving a request to monitor pressure, setting acontrol signal to indicate the first state and storing a first digitalpressure measurement and subsequently setting the control signal toindicate the second state and storing a second digital pressuremeasurement.
 12. The method of claim 11, further comprising: selectingone of the first and second digital pressure measurements and providingthe selected digital pressure measurement in response to the request tomeasure the pressure.
 13. The method of claim 10, wherein in the firststate the analog pressure signal is based on an output signal of thepressure sensor amplified by a first gain and wherein in the secondstate the analog pressure signal is based on the output signal from thepressure sensor amplified by a second gain.
 14. The method of claim 13,further comprising: determining to apply the first set of calibrationcoefficients, when the output signal from the pressure sensor is lowerthan a threshold, and determining to apply the second set of calibrationcoefficients, when the output signal from the pressure sensor is greaterthan the threshold.